With constant evolution of wireless communications technologies such as 2G, 3G, and 4G, exponentially increasing requirements of people for data services (especially after intelligent terminals emerge on the market), a rapid increase in a quantity of mobile users, and an increasingly large quantity of high buildings, requirements for traffic density and coverage are continuously increasing. A single antenna needs to bear more frequency bands, and more frequency bands and carriers need to be transmitted on a feeder.
However, as frequency bands and carriers increase, a problem of passive intermodulation becomes more prominent. When radio frequency signal powers at two or more frequencies simultaneously occur on a passive radio frequency device, a passive intermodulation PIM product is generated. Such a product is a hybrid signal generated because of a nonlinearity characteristic of a heterogeneous material connection. Typically, a third-order product of passive intermodulation may exactly fall within an uplink frequency band or a receive frequency band of a base station; and the third-order product causes interference to a receiver, and in a serious case, may even make the receiver unable to work normally.
A specific interference case may be shown in FIG. 1. A horizontal coordinate in FIG. 1 represents a quantity of frequency bands supported by a single feeder, and a vertical coordinate in FIG. 1 represents a case of third-order hit reception. It can be learned from FIG. 1 that an increase in the quantity of frequency bands supported by the single feeder results in an exponential increase of cases of third-order hit reception.
In the prior art, the PIM problem is resolved mainly by eliminating occurrence of a frequency band combination that causes the PIM problem. For example, for input signals at 900 M, 1800 M, 2100 M, and 2600 M, because there are second-order, third-order, fourth-order, and fifth-order intermodulation products, an existing solution is that no feeders are shared between the low frequency 900 M and the high frequencies 180000 M, 2100 M, and 2600 M. In a feeder-limited scenario, a remote radio unit RRU needs to be mounted on a tower and/or a feeder needs to be added, to ensure that no feeders are shared between the low frequency goo M and the high frequencies 1800 M, 2100 M, and 2600 M.
However, in the prior-art solution, station design is complicated, and even a tower needs to be reinforced or a feeder needs to be added. Consequently, a frequency band auctioned by an operator is unusable on some tower stations, and high costs of tower reinforcement or feeder addition are caused.